1. Field of the Invention
The present invention relates to electroplating technology, and, more particularly, to a method of depositing metal on an insulation substrate.
2. Description of Related Art
In the conventional electroplating on an insulation substrate, the critical step of forming a metallization pattern is that a position to be formed with a metallization pattern on an insulation substrate needs to be electrically connected to a cathode (a negative electrode) performing a reduction such that metal ions in electroplating solution are deposited on the insulation substrate via the reduction. For example, if copper is to be electroplated on the specific position of an insulation substrate, the portion of the insulation substrate that is not be electroplated with copper is masked. Then the insulation substrate is placed in electroplating solution. The specific position of the insulation substrate is electrically connected to a negative electrode, and copper ions are then reduced on the specific position of the insulation substrate to form a metallization pattern.
In the electroplating technology, there are acidic and basic electroplating solutions, and the acidic electroplating solution is better for usage due to its compatibility. In the prior art, the resist layer, such as a dry film or a photoresist, has anti-acid property but has no anti-alkali property. In the basic electroplating solution, the dry film or the photoresist has poor attachment. Currently, electroplating with leading wires and cured resist layer are used in the basic electroplating solution for electroplating.
FIG. 1A to FIG. 1G are sectional views illustrating conventional metal deposition in the electroplating solution by using leading wires according to the prior art. As shown, a conductive layer 2 is sputtered on an insulation substrate 1, a resist layer 3 is applied to form a pattern 30 to be plated, and a leading wire 31 (shown in FIG. 1C′) is provided. In the electroplating of Cu, Ni and Ag, the acidic electroplating solution is used for electroplating Cu, and the basic electroplating solution is used for electroplating Ag, such that the two electroplating procedures need to be performed separately. The insulation substrate 1 is then placed in the acidic electroplating solution, and the resist layer 3 has anti-acid property and thus has desired attachment property to the substrate. After the copper 4 is deposited on the pattern 30 and on the leading wire 31 of the insulation substrate 1, the resist layer 3 and the exposed conductive layer 2 are removed. Then, as shown in FIG. 1G, the electroplating of Ni and Ag is performed respectively. For this process, the resist layer 3 has no anti-alkali property and thus needs to be removed, and the pattern 30 is electrically connected to the negative electrode via the leading wire 31, so as to complete the deposition of the Ni and Ag 5. In order to selectively plate a metal layer on the surface of the insulation substrate 1 in the basic electroplating solution, the metallization structure of the insulation substrate 1 includes the pattern 30 and the leading wire 31 which is electrically connected to the pattern 30. When the leading wire 31 having Cu, Ni and Ag between the two patterns 30 is formed, a dicing blade or laser light would be affected by the leading wire 31 during cutting and thus the blade edge may be destroyed once it is in touch with metal or the energy of laser spot is reflected by the leading wire 31 without absorption from the insulation substrate 1. Therefore, these two cutting machines will fail to completely separate the insulation substrate 1. Further, the patterns 30 are electrically connected to one another by the leading wire 31, such that the open circuit or short circuit test of each of the patterns 30 on the insulation substrate 1 cannot be performed due to the electrical connection formed by the leading wire 31.
FIG. 2 is a sectional view showing a cured resist layer for the electroplating according to the prior art. The electroplating shown in FIG. 2 is similar to that in FIG. 1. An insulation substrate 1 is provided, a conductive layer 2 and a resist layer 3 are formed to construct a pattern 30 to be plated (as shown in FIG. 2C′) and the electroplating is performed in the acidic electroplating solution to form the copper 4. At this time, the resist layer 3 is not removed and the resist layer 3 is cured by baking (as shown in FIGS. 2D and 2E, the resist layer 3 is cured to be the resist layer 3′). The electroplating of the nickel layer is subsequently performed, and then the substrate is provided in the basic electroplating solution, so as to form the deposition of the silver 5. In this method, the cured resist layer 3′ has a little anti-alkali property, such that it is necessary for the electroplating to be completed in a short period of time. For example, upon the development of the dry film the baking is performed before electroplating, or upon the development of the dry film the hard baking is formed to enhance curing, so as to improve the anti-alkali property of the dry film. However, this method has poor stability, and peeling of the resist layer may occur in the basic electroplating solution since the basic solution, NaOH, for example, is just used for removing the resist layer. Moreover, during removing the over cured resist layer 3′, residual films may stay in slots between metals. It is hard to completely clean those residual films.
Briefly, the metal electroplating in the basic solution should be further improved. Conventional leading wire method may cause a big problem during the cutting process with a dicer or a laser. On the other hand, using cured resist layer in the basic electroplating cannot provide a stable yield in production due to the film residue. There is a need to improve the electroplating in the basic electroplating solution, so as to simplify the processing and reduce the cost.